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Small, shy, but plentiful of paleobiogeographic information

The paleontological record on shallow facies of the islands in the middle of a wide ocean such as the Atlantic allows to better understand the paleobiogeography of certain species, in particular those that have an amphi-Atlantic distribution. This is the case for small encrusting barnacles (you really need to pay attention to the surface of the fossil coral heads to spot them) of the genus Ceratoconcha.

Ranging in age from the middle Miocene to the Pleistocene, specimens from Madeira (Porto Santo island), Canaries (Lanzarote island) and Cape Verde (Maio island) archipelagos, in the Macaronesian realm of the Eastern North Atlantic, are described, some for the first time, in a new article (published online today) in Palaeogeography, Palaeoclimatology, Palaeoecology. The reported research, conducted by an international team of paleontologists from the USA, the Philippines, Spain and Portugal, not only extend the paleobiogeographic range of the genus, but also allows to consider mechanisms for the dispersal of these barnacle larvae.

During the Neogene, the Atlantic circulation pattern was significantly different from present day conditions, particularly after the closure of Panama Isthmus, at the end of middle Pliocene, and the establishment of the Gulf Stream. Before that, there was significant equatorial circulation between the Atlantic and the Pacific but also between the Tethys (Mediterranean) and the Indian ocean.

This new data suggests the existence of a wide catch area for barnacle larvae crossing the Atlantic, following trade winds from east to west and forced eastwards by strong hurricanes, a very plausible scenario in a much warmer world than today.

“Coral-dwelling pyrgomatid barnacles (subfamily Ceratoconchinae) were widely dispersed throughout the Paratethys and Mediterranean seas as well as the Atlantic Ocean during the Neogene, but today are limited to the Western Atlantic. Herein, the paleobiogeographic origin and dispersal of the genus Ceratoconcha is studied based on a combination of field, taxonomic, and literature studies. The first confirmed appearances of Ceratoconcha occur in lower Miocene strata (Burdigalian) with two closely related species on both sides of the Atlantic in western France and Florida. Fossils from the Miocene of Lanzarote in the Canary Islands and Pleistocene of Maio in the Cape Verde islands extend the known geographical and temporal range of the Ceratoconcha barnacles in the eastern Atlantic. During the Neogene, dispersal of marine taxa was a two-way process due to tectonic changes both influencing oceanic circulation and appearance and disappearance of oceanic islands. During the early Miocene, gyre formation was weak and the Atlantic Ocean mid-latitudes were warmer than today. This resulted in increased hurricane activity and the expansion of hermatypic coral hosts farther north in the North Atlantic. Normal ocean circulation transported barnacle larvae from east to west, but currents generated by hurricanes may have transported them in the opposite direction towards the margins of the northeastern Atlantic. Islands in between abetted barnacle contact and dispersal. The temporal range for Ceratoconcha is extended considerably in the eastern Atlantic from the early Pliocene to the Pleistocene. The hermatypic host corals of Ceratoconcha suffered a severe decline in the eastern Atlantic and the Mediterranean after the Miocene. Corals were present during the Pliocene and Pleistocene in the Cape Verde Islands. This suggests that the southernmost oceanic islands acted as a tropical refuge for host corals and their likely barnacle symbionts.”

Lecturer, researcher, author and consultant in Geology and Paleontology, affiliated with diverse national and international scientific organizations. Portuguese coordinator of ProGEO. Director of NanoLab and Rocha Amiga. (read more about me)